from Tkinter import *

def askopenfilename():
    """ Prints the selected files name """
    # get filename, this is the bit that opens up the dialog box this will
    # return a string of the file name you have clicked on.
    filename = tkFileDialog.askopenfilename()
    if filename:
        # Will print the file name to the text box
        print filename

# a subclass of Canvas for dealing with resizing of windows
class ResizingCanvas(Canvas):
    def __init__(self,parent,**kwargs):
        Canvas.__init__(self,parent,**kwargs)
        self.bind("<Configure>", self.on_resize)
        self.height = self.winfo_reqheight()
        self.width = self.winfo_reqwidth()

    def on_resize(self,event):
        # determine the ratio of old width/height to new width/height
        wscale = float(event.width)/self.width
        hscale = float(event.height)/self.height
        self.width = event.width
        self.height = event.height
        # resize the canvas 
        self.config(width=self.width, height=self.height)
        # rescale all the objects tagged with the "all" tag
        self.scale("all",0,0,wscale,hscale)

def main():
    root = Tk()
    myframe = Frame(root)
    myframe.pack(fill=BOTH, expand=YES)
    
    mycanvas = ResizingCanvas(myframe,width=850, height=400, bg="red", highlightthickness=0)
    mycanvas.pack(fill=BOTH, expand=YES)

    button = Button(root, text='GetFileName', command=askopenfilename)
    # this puts the button at the top in the middle
    button.grid(row=1, column=1)
    
    # add some widgets to the canvas
    #mycanvas.create_line(0, 0, 200, 100)
    #mycanvas.create_line(0, 100, 200, 0, fill="red", dash=(4, 4))
    #mycanvas.create_rectangle(50, 25, 150, 75, fill="blue")

    # tag all of the drawn widgets
    #mycanvas.addtag_all("all")
    
    root.mainloop()

if __name__ == "__main__":
    main()